Pleural Effusion

Transudative — Starling-force failure, intact pleura

• Heart failure: the single most common cause of pleural effusion in the United States; elevated pulmonary capillary hydrostatic pressure drives filtrate across visceral pleura. Classically bilateral, right > left.
• **Cirrhosis (hepatic hydrothorax)**: ascitic fluid tracks through diaphragmatic defects into the pleural space; typically right-sided and may be large despite minimal ascites.
• Nephrotic syndrome, protein-losing enteropathy, severe malnutrition: hypoalbuminemia lowers plasma oncotic pressure.
• Atelectasis, constrictive pericarditis, SVC obstruction, peritoneal dialysis, myxedema, urinothorax: less common transudative mechanisms tested as distractors.

Exudative — increased permeability or impaired lymphatic clearance

• Parapneumonic effusion and empyema: bacterial pneumonia inflames the visceral pleura; the most common exudate overall.
• Malignancy: lung and breast carcinoma, lymphoma, and mesothelioma; pleural seeding plus mediastinal nodal obstruction of lymphatic drainage.
• Pulmonary embolism: usually exudative and small; effusion never excludes PE and never explains hypoxemia out of proportion to size.
• Tuberculosis: delayed hypersensitivity to mycobacterial antigen; lymphocyte-predominant with high adenosine deaminase.
• Intra-abdominal and esophageal disease: pancreatitis and Boerhaave syndrome produce left-sided amylase-rich exudates.
• Connective tissue disease: rheumatoid pleuritis (strikingly low glucose) and lupus serositis.
• Iatrogenic/other: post-CABG, Dressler syndrome, chylothorax from thoracic duct injury or lymphoma, drug-induced (amiodarone, nitrofurantoin, methotrexate, hydralazine/procainamide-associated lupus), Meigs syndrome (ovarian fibroma), yellow nail syndrome.

• Increased hydrostatic pressure — occurs in left-sided heart failure, constrictive pericarditis, and superior vena cava obstruction; fluid transudates into the pleural space when pulmonary capillary pressures exceed plasma oncotic pressure
• Decreased plasma oncotic pressure — seen in hypoalbuminemia (nephrotic syndrome, cirrhosis, malnutrition); reduced colloid osmotic pressure fails to retain fluid intravascularly
• Increased pleural membrane permeability — caused by inflammation or malignancy affecting the visceral or parietal pleura; exudative fluid rich in proteins leaks into the pleural space
• Lymphatic obstruction — malignant infiltration of mediastinal or hilar lymph nodes impairs drainage of pleural fluid, leading to accumulation
• Negative intrapleural pressure — maintained by pleural lymphatic drainage; disruption results in fluid accumulation even when other pressures are normal

• Dyspnea — the most common symptom, occurring when effusions compress lung parenchyma; typically exertional but may be at rest with large effusions; worsens with patient recumbency
• Pleuritic chest pain — sharp, pleurisy-type pain that worsens with deep inspiration or coughing; suggests pleural inflammation from infection, malignancy, or pulmonary embolism rather than simple transudation
• Dry cough — results from pleural irritation or compression of airways; may be prominent in malignant or infectious effusions
• Orthopnea and paroxysmal nocturnal dyspnea — classic for cardiac effusions due to heart failure; patient cannot lie flat without worsening dyspnea
• Physical examination findings — decreased breath sounds, dullness to percussion, reduced tactile fremitus, and Ewart sign (bronchial breathing above large effusion); unilateral findings help localize the effusion
• Asymptomatic discovery — small effusions often found incidentally on imaging in asymptomatic patients, particularly common in heart failure or malignancy
• Fever and septic picture — suggests parapneumonic effusion or empyema; patient appears acutely ill with productive cough

Imaging approach

• Chest X-ray (CXR) — initial imaging showing blunting of costophrenic angles; small effusions (>200 mL) appear as meniscus sign; larger effusions show opacification; layering on lateral decubitus film confirms free-flowing fluid and helps quantify size
• Chest CT with contrast — superior for visualizing loculated effusions, identifying septations, assessing pleural thickening (concerning for malignancy or chronic infection), and determining if effusion is dependent (gravity-dependent, likely transudative) or fixed
• Ultrasound — excellent bedside tool for detecting effusions as small as 50 mL, assessing for loculation, guiding thoracentesis, and differentiating septated fluid from consolidated lung

Thoracentesis and pleural fluid analysis

• Indicated when: effusion is unilateral, new, or of unclear etiology; patient is febrile; there is clinical suspicion of infection, malignancy, or other specific diagnosis
• Contraindications: severe thrombocytopenia (<20,000), INR >1.5 (relative), anticoagulation (relative), or inability to identify safe puncture site
• Light's criteria (exudate if ≥1 criterion met):
• Pleural protein/serum protein ratio >0.5
• Pleural LDH/serum LDH ratio >0.6
• Pleural LDH >two-thirds upper limit normal serum LDH
• Cell count and differential — neutrophil-predominant suggests acute infection or pulmonary embolism; lymphocyte-predominant indicates chronic infection (tuberculosis, fungal), malignancy, or rheumatologic disease
• Glucose level — low glucose (<60 mg/dL) highly specific for rheumatoid arthritis, empyema, or esophageal rupture
• pH — acidic pH (<7.20) suggests complicated parapneumonic effusion or empyema requiring drainage
• Lactate dehydrogenase (LDH) — elevated in exudates; very high levels (>1000 IU/L) suggest malignancy or infection
• Cytology — can identify malignant cells but has limited sensitivity (60%); adenocarcinoma and lymphoma are most commonly detected
• Culture and Gram stain — bacterial culture positive in only 5-10% of parapneumonic effusions; send for bacterial, fungal, and mycobacterial cultures
• Additional studies based on clinical suspicion: ANA and LE prep (lupus), rheumatoid factor (rheumatoid arthritis), amylase (pancreatitis or esophageal rupture), cholesterol crystals (rheumatoid arthritis or tuberculosis), pleural biopsy for granulomas or malignancy

Management depends on underlying etiology and clinical significance

First-line treatment — address underlying cause

• Heart failure — diuretics (furosemide 40-80 mg PO daily, titrate to effect), ACE inhibitors, beta-blockers, and aldosterone antagonists; most effusions resolve with optimization of cardiac function
• Parapneumonic/uncomplicated effusion — treat underlying pneumonia with antibiotics alone; effusion typically resorbs with antibiotic therapy
• Malignant effusion — directed chemotherapy or targeted therapy for primary malignancy when possible; systemic treatment may cause effusion regression
• Pulmonary embolism — anticoagulation with DOAC (apixaban, rivaroxaban) or warfarin (target INR 2-3); effusion typically resolves with adequate anticoagulation

Therapeutic thoracentesis

• Indicated for: dyspnea attributable to effusion, need for diagnostic fluid analysis when effusion is large, or symptomatic relief when underlying cause cannot be rapidly treated
• Procedure: typically remove 1-1.5 L at initial procedure to reduce risk of re-expansion pulmonary edema; patient position seated leaning forward or supine; ultrasound-guided preferred; monitor for hypotension, cough, chest pain
• Complication risk: pneumothorax (rare, <1%), hemothorax, infection, re-expansion pulmonary edema (if >1.5 L removed rapidly)

Tube thoracostomy (chest tube)

• Indicated for: empyema (infected effusion), complicated parapneumonic effusion with loculation, hemothorax, or chylothorax

Complications of the effusion itself

• Complicated parapneumonic effusion and empyema (emergency): bacterial invasion consumes glucose and generates lactate, producing pH below about 7.20, low glucose, and high LDH; frank pus or a positive Gram stain defines empyema. Antibiotics alone will not sterilize a loculated space — the ACCP parapneumonic effusion guidance and IDSA/ATS pneumonia guidance both call for drainage.
• Fibrothorax and trapped lung: organizing fibrin deposition forms a restrictive pleural peel; the signal is failure of the lung to re-expand after drainage, with persistent basilar volume loss and a restrictive pattern on PFTs. Decortication may be required.
• Bronchopleural fistula: necrotizing infection erodes into airway; suspect with a persistent air leak and continuous bubbling in the chest-tube water seal.
• Respiratory failure and hemodynamic compromise (emergency): a massive effusion compresses lung and, rarely, shifts the mediastinum away from the effusion, impairing venous return. Contralateral tracheal deviation with hypotension demands urgent drainage.
• Sepsis and metastatic infection (emergency) from an undrained infected space.

Complications of treatment

• Re-expansion pulmonary edema: rapid removal of large volumes causes reperfusion injury and increased capillary permeability in the collapsed lung; presents as cough, chest tightness, and unilateral infiltrate within hours. This is why initial drainage is limited in volume and stopped for chest discomfort.
• Pneumothorax and hemothorax (hemothorax is an emergency): needle passage above the superior rib margin avoids the intercostal neurovascular bundle, which is tortuous in elderly patients; ultrasound guidance lowers risk.
• Organ puncture: liver or spleen laceration from an overly inferior insertion site.
• Indwelling pleural catheter infection and pleurodesis failure: recognized risks in the ATS/STS/STR malignant effusion guideline; fever with catheter-site erythema or new loculation signals it.
• Talc-related systemic inflammation/ARDS: reported with small-particle talc.

• Light's criteria are sensitive, not specific: they misclassify roughly a quarter of diuresed heart-failure transudates as exudates. If the clinical picture screams heart failure but Light's says exudate, calculate the serum-minus-pleural albumin gradient — greater than about 1.2 g/dL supports a transudate.
• pH is the action item: in a febrile patient with pneumonia and an effusion, pleural fluid pH below approximately 7.20, glucose below roughly 60 mg/dL, positive Gram stain, loculation, or frank pus means the single best next step is tube thoracostomy, not more antibiotics (ACCP parapneumonic guidance; IDSA/ATS 2019). Send fluid for pH in a heparinized blood-gas syringe on ice.
• Milky fluid: triglycerides above roughly 110 mg/dL define chylothorax — think thoracic duct injury after thoracic surgery, or lymphoma. Cholesterol crystals instead suggest a chronic pseudochylothorax (old TB or rheumatoid effusion).
• The lowest glucose on the wards: rheumatoid pleuritis and empyema. Very low glucose plus very low pH plus high amylase (salivary isoenzyme) after retching equals Boerhaave syndrome — a surgical emergency, not a pleural problem to tap and observe.
• Lymphocyte-predominant exudate with elevated adenosine deaminase points to tuberculous pleuritis; fluid AFB smear and culture are low-yield, so pleural biopsy showing caseating granulomas is the classic confirmatory move.
• The association examiners love: Meigs syndrome — benign ovarian fibroma with ascites and right pleural effusion that resolves after tumor resection.
• Common distractor: bilateral, symmetric effusions in a patient with obvious decompensated heart failure do not need a tap — diurese first. Conversely, do not attribute a unilateral effusion, fever, or pleuritic pain to heart failure without sampling.
• Cytology is imperfect: a single negative cytology does not exclude malignancy; the ATS/STS/STR malignant effusion guideline supports repeat sampling or pleuroscopic biopsy when suspicion remains.